Cooling Assembly for Cooling Heat Generating Component

ABSTRACT

A cooling assembly for cooling of a heat generating component ( 5 ) is provided. The cooling assembly comprises a heat sink ( 1 ) and at least one thermally conductive plate ( 2 ) attached to one side of the heat sink, where the plate is adapted to be in direct thermal contact with the heat generating component. The cooling assembly comprises at least one elongated heat conductor ( 3 ), which at least partly is embedded into the heat sink. The cooling assembly also comprises a plurality of fins ( 4 ) protruding from the heat sink. In the cooling assembly, the plate is at least partly embedded into the heat sink, and at least one of the heat conductors is adapted to be in direct thermal contact with the heat generating component.

TECHNICAL FIELD

The present invention relates to a cooling assembly for cooling a heatgenerating component, and a method of manufacturing a cooling assemblyfor cooling a heat generating component, as well as a coolingarrangement comprising such a cooling assembly, wherein the coolingassembly comprises a heat sink, at least one thermally conductive plate,at least one elongated heat conductor with elongated shape as well as aplurality of fins.

BACKGROUND

When products comprising electronic equipment are manufactured today,heat dissipation is an important issue. In order to manufacture morecompact products, the components inside the electronic equipment have asmaller size, but they still dissipate high amounts of heat that have tobe dealt with. Further, the products must not be too heavy, and mustfunction in an outdoor environment. Thus, when manufacturing coolingassemblies for cooling of electronic equipment, the volume and theweight should be considered, and they also have to be able toefficiently dissipate high amounts of heat in an environment where theyare exposed to rain, sun etc.

An example of electronic equipment that has to be efficiently cooled isa remote radio unit (RRU) in a radio base station (RBS). These RRUs arenormally installed outdoors on top of a tower or pole, which means thatthe requirements for volume and weight are critical, as well as theyhave to withstand a harsh outdoor environment. Since a long life time isdesirable for the cooling assembly of the RRU, a cooling by naturalconvection is preferred. When cooling by forced convection is applied,the use of e.g. a fan is necessary, and a fan is not able to withstand along lifetime in an outdoor environment.

The heat generation of the RRU itself may from time to time be over 400W. Further, a power amplifier board is located in the RRU, and the poweramplifier will generate a high amount of heat while working. Thegeneration of heat from the power amplifier board may reach over 150W/cm².

WO 2005/089197 A2 describes a power amplifier assembly that comprises anelectronics module, a finned heat sink and a heat pipe enhanced pallet,where the electronics module is mounted on the pallet and the pallet ismounted on the finned heat sink. On the power amplifier are componentsthat dissipate heat mounted. The components are attached to a coppertungsten flange to facilitate the heat conduction to the heat sink andthe heat pipe.

This known power amplifier assembly is only able to dissipate limitedamounts of heat and is relatively heavy. Further, the thermal resistanceof the copper tungsten flange will decrease the heat transfer rate ofthe heat pipe. Thus, there is a need for an improved cooling assembly.

SUMMARY

The object of the present invention is to address the problem outlinedabove, and this object and others are achieved by the apparatus and themethod according to the appended independent claims, and by theembodiments according to the dependent claims.

According to a first aspect, the invention provides a cooling assemblyfor cooling of a heat generating component. The cooling assemblycomprises a heat sink with a first side adapted to face the heatgenerating component and a second side that is opposite the first side.Further, the cooling assembly comprises at least one thermallyconductive plate attached to the first side of the heat sink and wherethe plate is adapted to be in direct thermal contact with the heatgenerating component. The cooling assembly also comprises at least oneheat conductor with an elongated shape and where the heat conductor isat least partly embedded into the first side of the heat sink. Thecooling assembly also comprises a plurality of fins protruding from thesecond side of the heat sink. In the cooling assembly is the plate atleast partly embedded into the heat sink on the first side and at leastone of the heat conductors is adapted to be in direct thermal contactwith the heat generating component.

Thus, an advantage with the cooling assembly is that the heat generatingcomponent is efficiently cooled by a combination of the heat sink, thethermally conductive plate, the elongated heat conductor and the coolingfins. Since the plate is embedded into the heat sink the coolingassembly gets a compact design. By letting the heat conductor be indirect thermal contact with the heat generating component, the heattransfer rate of the heat conductor will be efficient, which isadvantageously.

At least one of the heat conductors may be a heat pipe. In order to havea high heat transfer rate in the heat pipe from the heat generatingcomponent, at a hot region of the heat sink, to a cooler region of theheat sink, the heat pipe or heat pipes may be adapted to be in directthermal contact with the heat generating component. A direct thermalcontact between the heat generating component and the heat pipe has theadvantage that it leads to efficient cooling of the heat generatingcomponent.

Normally, when using heat pipes in cooling applications, there might beproblems during a cold start when the material used inside the heat pipemay freeze. In this cooling assembly the heat pipe will not be disabledduring cold start even if the liquid material inside has frozen. Thus,it is advantageously using a heat pipe in the assembly according to theapplication, since the cooling will be enabled even if the heat pipe isfrozen, i.e. the heat pipe will have a cooling capacity as a heat sink.

The thickness of the heat sink may be non uniform. Further, a region ofthe heat sink may have a greater thickness and this region may at leastcomprise the location of the plate, which also may be the region of theheat sink that is closest to the heat generating component. The regionof the heat sink with greater thickness may extend between two oppositesubstantially parallel edges, but the region may also extend in anotherdirection. The thickness of the heat sink may decrease continuously in adirection parallel to the said two opposite edges, or the thickness maydecrease in another direction.

At least a part of at least one heat conductor may be embedded into theplate. When the heat conductor is a heat pipe at least a part of thisheat pipe may be embedded into the plate. This design is advantageouslyin order to be able to manufacture a compact and efficient coolingassembly.

The fins may extend between two opposite substantially parallel edges.As is the case with the region of the heat sink that is thicker, thefins may also extend in another direction. But the manufacturing of thecooling assembly is most efficient when the fins and the thicker regionof the heat sink extend in the same direction, e.g. between the said twoedges.

The fins may be spaced apart with a distance of approximately 10 to 14mm. Thereby is the air flow around the cooling assembly optimized, whichleads to the most efficient cooling, and thus is advantageously.

Further, the plate may have a greater area than the heat generatingcomponent. Depending on the amount of heat generated by the heatgenerating component, the plate may not necessarily have a greater area,and the area may e.g. have substantially the same area as the heatgenerating component. Thus, it is an advantage that depending on theamount of heat generated the size of the plate may be varied.

The plate may be made of copper, but could also be manufactured in anyother appropriate material with a high heat transfer rate, in order toefficiently lead away heat from the heat generating component. Thematerial could also be another material e.g. tungsten or a mixture ofdifferent materials.

The heat sink may be made of aluminum or magnesium. The fins may also bemade of aluminum or magnesium. Other light weight materials with anacceptable heat transfer rate are also possible to use whenmanufacturing the heat sink and the fins. Since the heat sink and thefins form large parts of the cooling assembly, a main issue whenchoosing material for these parts is the weight of the materials.However, they should also have a good enough heat transfer rate to beable to lead away heat from the heat generating component.

According to a second aspect, the invention provides a coolingarrangement that comprises a heat generating component attached to thecooling assembly, according to the first aspect.

According to a third aspect, the invention provides a method ofmanufacturing a cooling assembly. The method comprises providing a heatsink with a plurality of fins protruding from one side of the heat sinkand embedding a plate in the heat sink on the side of the heat sink thatis opposite the side from which the fins protrude. The method furthercomprises providing elongated grooves on the side of the heat sink thatis opposite the side from which the fins protrude. The method alsocomprises inserting elongated heat conductors into the grooves andattaching the heat conductors to the heat sink. The method furthercomprises filling the gaps around the heat conductors and machining thesurface of the side of the heat sink that is opposite the side fromwhich the fins protrude. Thus, the cooling assembly is manufactured inan efficient way, which may limit the costs of production and thus, isan advantage of the invention.

The method may further comprise attaching a heat generating component tothe cooling assembly so the heat generating component is in directthermal contact with the plate and the heat conductors. This has theadvantage to more efficiently lead away the heat from the heatgenerating component.

The method may also comprise attaching of the heat conductors to theheat sink by welding and filling the gaps around the heat conductorswith solder. This leads to a good thermal contact, which is a furtheradvantage.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, and withreference to the accompanying drawings, in which:

FIG. 1 illustrates a perspective view of the cooling assembly;

FIG. 2 illustrates a cross sectional view of a part of the cut along A-Ain FIG. 1, and where the fins are omitted;

FIG. 3 illustrates a cross section of a part of the heat sink with fins;and

FIG. 4 is a flowchart of the method of manufacturing the coolingassembly.

DETAILED DESCRIPTION

In the following description, the invention will be described in moredetail with reference to certain embodiments and to the accompanyingdrawings. For purposes of explanation and not limitation, specificdetails are set forth, such as particular scenarios, techniques, etc.,in order to provide a thorough understanding of the present invention.However, it is apparent to one skilled in the art that the presentinvention may be practised in other embodiments that depart from thesespecific details.

A basic idea with the invention is to efficiently cool a heat generatingcomponent by a cooling assembly comprising a heat sink, at least onethermally conductive plate, at least one elongated heat conductor and aplurality of fins. The cooling assembly should have a light weight andshould be able to efficiently cool a component in an outdoorenvironment. The heat generating component may e.g. be the electronicequipment in a remote radio unit in a radio base station or theelectronic equipment in any other product that is used outdoors orelsewhere.

FIG. 1 illustrates an exemplary embodiment of the cooling assembly in aperspective view. In one embodiment, the heat sink 1 is made of aluminumor magnesium and the fins 4 are made of aluminum or magnesium as well.In another embodiment, the heat sink 1 and the fins 4 are made ofanother light weight material with a certain heat transfer rate. Theheat sink 1 and the fins 4 may be manufactured by the same material orby different materials.

As can be seen in FIG. 1, the heat sink and the fins constitute a largepart of the cooling assembly. Therefore, the weight of the materialschosen for these parts is preferable comparatively low. Another aspectis the heat transfer rate, and since the heat sink and the fins shouldbe able to transfer heat away from the heat generating component, theirheat transfer rate is preferable comparatively high.

The heat sink 1 has a first side 9 and a second side 10 that is oppositethe first side. The heat sink has two opposite substantially paralleledges 6 and 7.

FIG. 1 shows an exemplary embodiment of the invention where the coolingassembly comprises four heat conductors 3 with elongated shape. Thenumber of heat conductors may be greater or lower, depending on theamount of heat that must be dissipated. These elongated heat conductors3 are preferably made of a material with a high heat transfer rate, e.g.copper. The heat conductors 3 are embedded in the first side 9 of theheat sink so that one end of the heat conductors is able to be in directthermal contact with the heat generating component 5. The elongated heatconductors 3 transfer heat from the end, which is in direct thermalcontact with the heat generating component, to the other end of theelongated heat conductors 3, i.e. to the end which is situated at acooler region of the heat sink 1. The thermally conductive plate 2 ispreferably also made of a material with a great heat transfer rate, e.g.copper.

FIG. 2 illustrates a cross sectional view of a part of the coolingassembly along A-A in FIG. 1. The fins have been omitted for the sake ofclarity. In a preferred embodiment, the area of the thermally conductiveplate 2 is greater than the area of the heat generating component 5. Thesize of the plate depends on the amount of heat generated by the heatgenerating component. According to an exemplary embodiment, the area issubstantially the same as the area of the heat generating component.According to another exemplary embodiment, which is not illustrated inFIG. 2, the area is smaller than the area of the heat generatingcomponent. In the preferred embodiment of the invention shown in FIG. 2,the plate 2 is embedded in the heat sink 1, so that the surface of thethermally conductive plate 2 is flush with the first side 9 of the heatsink. According to another exemplary embodiment, the plate is onlypartly embedded in the heat sink.

In order to achieve a good direct thermal contact between the heatgenerating component 5 and the heat conductors 3 no air gaps are allowedin the cooling assembly. As illustrated in the preferred embodiment ofthe invention in FIG. 2, the gaps around the heat conductors 3 arefilled with a bonding material 11.

As described above, the FIGS. 1 and 2 show a cooling assembly accordingto an exemplary embodiment of the invention. The drawings show aplurality of elongated heat conductors 3. However, the invention is notlimited to a plurality of heat conductors, instead, depending on theamount of generated heat, there might be a fewer number of heatconductors 3, e.g. only one heat conductor. The elongated heat conductortransfers heat from a hot region of the heat sink to a cooler region,thus it is preferably made of a material with a high heat transfer ratee.g. copper. According to an exemplary embodiment, at least one of theheat conductors 3 is a heat pipe. A heat pipe is an efficient coolingcomponent that consists of an elongated hollow member, e.g. a pipe,which is manufactured in a material with a high heat transfer rate andfilled with a liquid material that is able to condense at the hot endand evaporate at the cold end. The material of the heat pipe is e.g.copper, or any other material with a high heat transfer rate and theliquid material is for example water.

The cooling assembly according to the exemplary embodiment of theinvention illustrated in FIGS. 1 and 2 has a region 8 with a greaterthickness, comprising the location of the plate 2. This region extendsbetween the two opposite edges 6 and 7, and the thickness of the regiondecreases continuously in a direction parallel to the said two oppositeedges 6 and 7.

FIG. 3 illustrates a cross section of a part of an exemplary heat sinkwith fins where the thickness T of the heat sink is shown at a regionthat does not comprise the region 8, i.e. a part of the heat sink nearthe edges. The area of the fins 4 is preferably as large as possible inorder to spread the heat from the heat generating component 5. Accordingto an exemplary embodiment of the invention, the fins are spaced apartwith a distance d of approximately 10 to 14 mm, which is ideal foroptimizing the air flow around the heat sink, and leads to the mostefficient cooling by natural convection. However, another distancebetween two subsequent fins is also possible. The thickness t of thefins 4 is preferably as thin as possible. Depending on the manufacturingtechnique, the thickness is e.g. 1 and 2 mm. The height h of the fins 4also depends on the technique of manufacturing. The height is preferablywithin a range from e.g. 60 to 120 mm. The length of the fins 4, i.e.the distance between the two opposite edges 6 and 7, in the exemplaryembodiment of the invention shown in FIG. 1, is e.g. between 300 and 700mm. The thickness T of the heat sink 1 near the edges is e.g. 7 to 10mm, and according to an exemplary embodiment, the thickness increasescontinuously towards the region 8, which is e.g. about twice as thick asthe heat sink near the edges.

FIG. 4 is a flowchart illustrating an exemplary method of manufacturinga cooling assembly, according to the invention. In one preferredembodiment, the heat sink 1 and the fins 4 are manufactured byextrusion. This technique is e.g. used when the material of the heatsink and the fins is aluminum. In another preferred embodiment, the heatsink 1 and the fins 4 are manufactured by die casting. This technique ise.g. used when the material of the heat sink and the fins is magnesium.Other manufacturing techniques to provide, in step 20, the heat sink 1with the fins 4 protruding from the second side 10 are also possible.

The thermally conductive plate 2 is embedded, in step 21, in the heatsink 1 on the first side 9 by machining a recess in the heat sink withthe size of the plate 2, and thereafter embedding the plate 2 in therecess. According to a further exemplary embodiment, the recess istreated with a bonding material with a high heat transfer rate, such asthermally conductive epoxy or solder, before embedding the plate, inorder to achieve a good thermal contact between the plate and the heatsink. After the plate has been embedded, grooves are provided, in step22, on the first side 9 of the heat sink. The grooves are machined andmay also be treated with a bonding material with a high heat transferrate before the heat conductors 3 are inserted, in step 23, into thegrooves. The heat conductors 3 are attached, in step 24, to the heatsink 1 by means of a bonding material, e.g. by welding.

The gaps around the heat conductors 3 are filled, in step 25, by abonding material, e.g. solder. FIG. 2 illustrates the bonding material11 at the heat conductors 3. The surface of the first side 9 of the heatsink 1 is machined, in step 26, to achieve a flat surface. Thereafter,the heat generating component 5 is attached in direct thermal contactwith the thermally conductive plate 2, as well as with the heatconductors 3.

In order to ensure an efficient cooling assembly, and to assure a goodthermal contact between the heat generating component 5 and the plate 2,as well as the heat conductors 3, it is important that no air voidsremain in the assembly. Preferably, all air voids should be filled witha thermal conductive bonding material, such as solder, weld, thermallyconductive epoxy or any other suitable bonding material.

Further, the above mentioned and described embodiments are only given asexamples and should not be limiting to the present invention. Othersolutions, uses, objectives, and functions within the scope of theinvention as claimed in the accompanying patent claims should beapparent for the person skilled in the art.

1-20. (canceled)
 21. A cooling assembly for cooling a heat generatingcomponent, comprising: a heat sink having a first side adapted to facethe heat generating component, and a second side that is opposite thefirst side; at least one thermally conductive plate attached to and atleast partially embedded into the first side of the heat sink, whereinthe plate is adapted to be in direct thermal contact with the heatgenerating component; a first heat conductor having an elongated shape,wherein the first heat conductor is at least partly embedded into thefirst side of the heat sink; a plurality of fins protruding from thesecond side of the heat sink; wherein the first heat conductor isadapted to be in direct thermal contact with the heat generatingcomponent.
 22. The cooling assembly of claim 21 wherein the first heatconductor is a heat pipe.
 23. The cooling assembly of claim 21 whereinthe heat sink has a non uniform thickness.
 24. The cooling assembly ofclaim 21 wherein the heat sink has a first region that has a greaterthickness than a second region of the heat sink; wherein the plate isdisposed in the first region.
 25. The cooling assembly of claim 24wherein the first region of the heat sink extends between two oppositesubstantially parallel edges of the heat sink.
 26. The cooling assemblyof claim 25 wherein a thickness of the heat sink decreases continuouslyfrom the first region to the second region in a direction parallel tothe two opposite edges.
 27. The cooling assembly of claim 21 wherein atleast a part of the first heat conductor is embedded into the plate. 28.The cooling assembly of claim 21 wherein the fins extend between twoopposite substantially parallel edges of the heat sink.
 29. The coolingassembly of claim 21 wherein the fins are spaced apart at a distance ofapproximately 10 to 14 millimeters.
 30. The cooling assembly of claim 21wherein the plate has a greater area than the heat generating component.31. The cooling assembly of claim 21 wherein the plate is made ofcopper.
 32. The cooling assembly of claim 21 wherein the heat sink ismade of aluminum or magnesium.
 33. A method of manufacturing a coolingassembly, comprising: providing a heat sink having a first side and anopposite second side, and having a plurality of fins protruding from thesecond side; embedding a plate into the first side of the heat sink;providing elongated grooves on the first side of the heat sink;inserting elongated heat conductors into the grooves; attaching the heatconductors to the grooves of the heat sink; filling gaps in the groovesof the heat sink around the heat conductors with a bonding material; andmachining a surface of the first side of the heat sink.
 34. The methodof claim 33 further comprising attaching a heat generating component tothe cooling assembly so that the heat generating component is in directthermal contact with the plate and the heat conductors.
 35. The methodof claim 33 wherein the heat conductors are attached to the heat sink bywelding.
 36. The method of claim 33 wherein the bonding material issolder.